The invention relates to a plasma reactor for generating and maintaining a plasma, specifically for deposition of diamond, comprising a frequency generator and a resonant cavity to which electromagnetic waves are fed by the frequency generator, with a reaction unit being suited for introduction in the resonant cavity bounded by a wall, in a region of high field strength.
Such a plasma reactor is known from the publication "Diamond Deposition Technologies" by P. K. Bachmann and W. van Enckevort, published in the magazine Diamond and Related Materials, volume 1, pages 1021 through 1034, in 1992. In this plasma reactor, microwaves generated by means of a frequency generator are via a pin type coupler introduced in a resonant cavity which is fashioned as a resonant cylinder formed by a cylindrical pipe closed endwise. On the sealed end of the resonant cylinder, opposite the pin type coupler, there is a reaction unit arranged with a substrate to be coated from a gas phase formed by an ignited plasma.
In the prior plasma reactor, the situation and shape of the plasma depends very sensitively on process parameters such as gas pressure and coupled microwave power. Moreover, these two process parameters are not selectable independently of one another, but are adjustable in mutual dependence only within a relatively narrow correlation range. Leaving the correlation range occasions frequently an abrupt spatial displacement of the plasma, which, besides disturbing the deposition process, destroys within a short time, e.g., a quartz glass enclosing the substrate and bounding the reaction volume.
A further disadvantage of the prior plasma reactor is its great dependence of the plasma situation on the geometric constraints and the arrangement of the reaction unit.
The objective underlying the invention is to create a plasma reactor which, with a mutually very extensively independent selection of process parameters such as gas pressure and coupled electromagnet power, is characterized by a spatially stable plasma that is homogeneously distributed over the deposition area of a substrate.